There had been father's Anglo-Indian friends before he quarrelled with them.

But after that she and Constantia never met a single man except clergymen.

How did one meet men?
Or even if they'd met them, how could they have got to know men well enough to be more than strangers?
One read of people having adventures, being followed, and so on.

But nobody had ever followed Constantia and her.

Oh yes, there had been one year at Eastbourne a mysterious man at their boarding-house who had put a note on the jug of hot water outside their bedroom door! But by the time Connie had found it the steam had made the writing too faint to read; they couldn't even make out to which of them it was addressed.
And he had left next day.